This invention relates to a fixture block serving as a manufacturing accessory, particularly for the machining of metal or similar workpieces, and adapted to be combined, through contacting surfaces, with further correspondingly designed accessories and to be instrumental in bringing workpieces to be machined into proper position or orientation for the particular machining operation, such as planing, milling, drilling and the like, and maintaining the workpieces in such proper position or orientation during at least one working cycle, the fixture block having horizontal and vertical contact surfaces designed as aligned rows of coplanar projecting areas separated by machined rows of coplanar recessed areas, the recessed areas being formed, for example, by planing, milling or the like operations.
Particularly for machining metal workpieces, it is well known to use correspondingly designed and suitable manufacturing accessories in the form of fixtures. The term "machining" is understood to include, substantially, manufacturing operations performed by boring, milling, planing, shaping, broaching, honing and grinding machines. Manufacturing accessories, in the form of fixtures, and which are used mainly in connection with the mentioned machines, serve primarily to reduce the machining time of the workpiece and the manufacturing costs of the part and of the completed unit, as well as to improve the quality of the machined part. In addition, they make is possible for unskilled persons and workers unfamiliar with the particular operation to perform high quality work. The manufacturing efficiency of the individual working steps and/or operations, as well as the efficiency of the machine, and thus also of the worker, depends largely on the purposeful construction of the respective fixture.
In course of time, certain basic rules have been established for the design of fixtures. In the following, as far as necessary, these rules are briefly specified since, hereinafter, the fixture underlying the present invention will be compared therewith:
1.0 The fundamental condition for a successful design of a manufacturing accessory is a close cooperation between the designer of the accessories and the planner of the manufacturing process.
2.0 The Design and construction of the accessory have to take into account the number of workpieces to be machined and the time of starting the manufacturing process, since both parameters are determining factors for the quality and costs of a fixture and, thus, for the manufacturing stage.
3.0 It must be checked whether so-called standard fixtures (general accessories), or already existing fixtures which, however, are no longer used at that time, can be adapted, provided that costs are saved thereby.
4.0 While designing and constructing fixtures, standardized constructional elements (such as clamping plates, angleplates, handles, screws, handwheels, etc.) are to be considered on a largest scale and the pertinent DIN and AWF standards, as well as, if necessary for supplementation, the corresponding factory standards which are to be used.
5.0 In taking into account a sufficient stiffness of shape, all fixtures are always to be designed as light in weight as possible in order not to unnecessarily fatigue the worker at work with the result of an aversion to the use of the fixtures.
6.0 Care must be taken to design the fixtures in a manner as simple as possible, with the shortest flow of stress in the clamping elements and to avoid any complicated and intricate mechanisms so as to obtain a clamping and unclamping time as short as possible. Moreover, in any case, a machined surface and, for oblique bores, auxiliary bores, are to be provided on the body of the fixture, to be able to start from these surfaces or bores while mounting the fixture and measuring.
7.0 The component parts of a fixture must not affect the visibility of the locations to be machined on the workpiece nor their accessibility. Also, the fixture bodies must be designed and the component parts arranged so as to permit an unhindered discharge of chips and of the coolant.
8.0 If possible, the first working sequence is to be provided so that the workpieces can be received, also during the subsequent operations in the following fixtures, by an already finish-machined surface, turned-off face, or bore.
9.0 With fixtures having to absorb higher working pressures, the clamping elements must never be arranged so as to be particularly stressed by the working pressure. Instead, they must always be positioned so that only portions fixed to or integral with the fixture are exposed to the load. In addition, the bearing area for the clamping elements is to be chosen so that a canting or tilting of the workpieces remains prevented, and that the workpieces are applied against the fixture only at locations with no mold or die seams, intakes, or ascending-tube sockets.
10.0 The clamping elements on a fixture are always to be chosen so as to avoid loose parts, such as wrenches, pins, wedges and hammers, whenever practicable, because an improper handling therewith may damage the fixture and jeopardize its working accuracy.
11.0 A fixture must always be designed so as to practically prevent any faulty insertion of the workpiece. Of course, in addition, a fixture also has to be accident-safe and fool-proof in operation. Moreover, a sufficient space must be provided for the fingers between the clamping elements and the fixture body as well as between the workpiece and the fixture to permit an insertion and removal of a workpiece without injuring fingers or hands.
12.0 Finally, drill-jig bushings or the like are to be positioned so as to have a certain spacing from the workpiece, particularly if the workpiece is of a light metal, yellow brass, etc. If possible, slip-renewable bushings are also to be avoided. While drilling holes having unequal diameters, the outer diameters of the slip-renewable bushings are to be determined so as to prevent a mistake and, thereby, scrapwork.
Fixtures serving as manufacturing expedients, which can be completed and used in the manner of a building-block system, are already known. Like the present invention to be explained hereinafter, such known building block systems substantially comprise basic elements, build-up elements, elements for determining the position, as well as clamping and connection elements.
As already indicated by the term "basic elements", such elements are of primary importance because the further building up of the system is fully determined by the basic elements and dependent thereon.
In a well-known fixture building-block system, aside from a base plate provided with crosswise extending T-grooves, a plurality of differently designed angle clamping plates are the fundamental elements of the building-block system:
One of the angle clamping plates, whose base intersects with the front surface at 90.degree., is provided, on its back side, with two stiffening ribs extending obliquely at an angle of approximately 25.degree. and blending, at both their lower and upper ends, into a clamping strip which is provided with a T-groove. Both the base and the front surface of the angle clamping plate are provided with T-grooves crossing each other. Five horizontal and three vertical T-grooves are provided in the front surface. The base is formed with two sets of three T-grooves, with the two sets of grooves crossing each other. At each point of intersection of the two surfaces, tapholes are provided in the groove bottom. The two stiffening ribs are provided with two holes having unequal diameters, which extend coaxially of the horizontal T-grooves provided in the front surface. The two holes are intended to reduce the weight of the clamping plate. It is evident that the angle clamping plate may also be used in a position turned through 90.degree., i.e., with the front surface forming the base and the smaller base forming the clamping or working surface.
A variant of the angle clamping plate just described substantially comprises a cast body closed at all sides and having a triangular shape where the third leg is inclined at an angle of approximately 30.degree.. This clamping plate is provided with crossing T-grooves on all sides. While the front surface, which is larger than the base, is provided with three horizontal and two vertical, mutually intersecting, rows of grooves, the base comprises only two rows of two grooves each in each axial or dimensional direction. The inclined surface comprised also two rows of mutually intersecting grooves, while the horizontal upper connection surface, between the front surface and the inclined surface, is provided with only one T-groove extending parallel to the horizontal grooves of the front surface. In the direction parallel to the bottom surfaces of the grooves, the clamping plate is provided with a through hole. Tapped holes are entirely absent, not only at the points of intersection of the T-grooves, but everywhere. Some through holes provided in the lateral limiting surfaces serve for the connection of the angle clamping plate with one or more other plates.
In principal, an immediately apparent drawback of the first described angle clamping plate is the fact that it has any variant at all. This means, on the one hand, that the plate is no basic element in the proper sense of the word and, on the other hand, that the use of the respective building-block system is unnecessarily made more expensive because a variant of the clamping plate, even several specimens, must be procured and stored.
Even if the just mentioned drawback could be tolerated after all, the use in principle of the T-grooved elements makes the entire building-block system so expensive that the effect of economization aimed at while using the system is nullified automatically. That is, it is evident and instantly clear to anyone skilled in the art that the careful manufacture of a necessarily large number of precision-machined T-grooves makes the structural parts of the system expensive to such an extent that, already for this very reason, a not insignificant number of potential users would probably desist from equipment with such building blocks.